Optical characteristic measuring apparatus

ABSTRACT

The present invention relates to an apparatus for the precision measurement of the optical characteristics of the eye and the shape of the cornea of the eye. An object of the present invention is to provide an optical characteristic measuring apparatus capable measuring the optical characteristics of an irregular astigmatism component. An illuminating optical system illuminates a minute region on the retina of the eye with light rays emitted by an illuminating light source, a reflected light guiding optical system guides reflected light rays reflected from the retina of the eye to a light receiving device, a converting device converts the reflected light rays into at least seventeen light beams, a light receiving device receives the plurality of light beams from the converting device, and an arithmetic unit determines the optical characteristics of the eye and the shape of the cornea on the basis of the inclination of the light rays determined by the light receiving device.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an apparatus for the precisionmeasurement of the optical characteristics of the eye and the shape ofthe cornea and, more particularly, to an optical characteristicmeasuring apparatus capable of measuring the optical characteristics ofan irregular astigmatism component.

[0002] A conventional optical characteristic measuring apparatus formeasuring the optical characteristics of the eye known as arefractometer is capable of expressing the optical characteristics ofthe eye merely as a spherical component, a regular astigmatism componentand the angle of the axis of the regular astigmatism component.

[0003] Some eyes have an irregular astigmatism component in addition toa regular astigmatism component. Irregular astigmatism cannot becorrected by a pair of spectacles if the quantity of the irregularastigmatism component is large, contact lens must be used instead of apair of spectacle lens, and the eye must be examined by a medicaldoctor.

[0004] However, the conventional optical characteristic measuringapparatus for measuring the optical characteristics of the eye, such asa refractometer, is used only for reforming a pair of spectacles and itsperformance is not fully satisfactory. Accordingly, desired eagerly wasan appearance of an optical characteristic measuring apparatus capableof accurately measuring the irregular astigmatism component of the eyein addition to the spherical component, the regular astigmatismcomponent and the angle of the axis of the regular astigmatism component

SUMMARY OF THE INVENTION

[0005] An optical characteristic measuring apparatus according to oneaspect of the present invention comprises an illuminating optical systemfor illuminating a minute region on the retina of the eye with lightemitted by an illuminating light source; a light receiving opticalsystem for receiving light reflected from the retina of the eye andguiding the reflected light to a light receiving device; a convertingdevice for converting the reflected light into at least seventeen lightbeams and sending the light beams to the light receiving device; and anarithmetic unit for determining the optical characteristics of the eyeand the shape of the cornea of the eye on the basis of the inclinationof light rays fallen on the light receiving device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]FIG. 1A is a block diagram of an optical characteristic measuringapparatus in a first embodiment according to the present invention;

[0007]FIG. 1B is a front view of a variable diaphragm included in theoptical characteristic measuring apparatus of FIG. 1;

[0008]FIG. 2 is diagrammatic view of assistance in explaining theprinciple of the optical characteristic measuring apparatus of FIG. 1;

[0009]FIG. 3 is a diagrammatic view of assistance in explaining a methodof directly indicating power based on quantity and orientation relatingto maximum curvature and minimum curvature;

[0010]FIG. 4 is a pictorial view of assistance in explaining a method ofindicating meridional power;

[0011]FIG. 5 is a pictorial view of assistance in explaining a method ofindicating meridional power;

[0012]FIG. 6 is a graph of assistance in explaining a method ofimproving the accuracy of position measurement;

[0013]FIG. 7(a) is a diagrammatic view of assistance in explaining amethod of discriminating between an image formed by light reflected fromthe retina and an image formed by light reflected from the cornea;

[0014] FIGS. 7(b) to 7(d) are graphs of assistance in explaining amethod of discriminating between an image formed by light reflected fromthe retina and an image formed by light reflected from the cornea;

[0015]FIG. 8 is a diagrammatic view of assistance in explaining a liquidcrystal device;

[0016]FIG. 9 is a diagrammatic view of an optical characteristicmeasuring apparatus in a third embodiment according to the presentinvention;

[0017]FIG. 10 is a diagrammatic view of an optical characteristicmeasuring apparatus in a fourth embodiment according to the presentinvention;

[0018]FIG. 11 is a block diagram showing the electrical configuration ofthe optical characteristic measuring apparatus in the fourth embodiment;

[0019]FIG. 12 is a block diagram showing the electrical configuration ofthe optical characteristic measuring apparatus 10000 in the fourthembodiment;

[0020]FIG. 13 is a flow chart of assistance in explaining XY alignment;

[0021]FIG. 14 is flow chart of assistance in explaining Z alignment;

[0022]FIG. 15 is a diagrammatic view of assistance in explainingalignment;

[0023]FIG. 16 is a flow chart of assistance in explaining the principle;

[0024]FIG. 17 is a diagrammatic view of an optical characteristicmeasuring apparatus in a fifth embodiment according to the presentinvention;

[0025]FIG. 18 is a diagrammatic view of the optical characteristicmeasuring apparatus in the fifth embodiment; and

[0026]FIG. 19 is a pictorial view of assistance in explaining thefunction of an optical characteristic measuring apparatus in amodification of the optical characteristic measuring apparatus in thefirst embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] First Embodiment

[0028] Referring to FIG. 1A, an optical characteristic measuringapparatus in a first embodiment according to the present inventioncomprises an illuminating light source 100, an illuminating opticalsystem 200 for illuminating a minute region on the retina of the eye1000 with light rays emitted by the light source 100, a light receivingdevice 500 which receives light rays reflected from the retina of theeye 1000, a reflected light guiding optical system 300 for guiding lightrays reflected from the retina of the eye to the light receiving device500, a converting device 400 which converts the reflected light raysinto at least seventeen light beams which are received by the lightreceiving device 500, and an optical characteristic calculating unit 600which determines the optical characteristics of the eye 1000 on thebasis of the inclinations of the light beams determined by the lightreceiving device 500.

[0029] A controller 800 controls operations of -the whole electricalconfiguration of the optical characteristic measuring apparatusincluding the optical characteristic calculating unit 600. Thecontroller 800 controls and drives the light source 100 through a lightsource driving unit 101.

[0030] It is desirable that the light source 100 is capable of emittinglight having a high spatial coherence and a low temporal coherence. Thelight source 10 of the first embodiment is a STD (superluminescentdiode), which is a point light source having a high luminance.

[0031] The light source 100 need not be limited to the SLD (SuperLuminescent Diode); a laser which emits light having a high spatialcoherence and a high temporal coherence can be employed as the lightsource 100 if a rotary diffuser or the like is inserted in an opticalpath to lower the temporal coherence properly.

[0032] Although both the spatial coherence and the temporal coherence ofthe light emitted by a light source such as led are low, it can be usedif a pinhole or the like is disposed at a position corresponding to thelight source on the light path, provided that it emits a large quantityof light.

[0033] The wavelength of the light emitted by the illuminating lightsource 100 of the first embodiment may be equal to, for example, that ofthe E line at the middle of the visible region. Although it is desirableto use the E line, which is a reference wavelength for spectacles, formeasurement, the D line may be used for measurement when the opticalcharacteristic measuring apparatus is used in the USA.

[0034] The illuminating optical system 200 illuminates a minute regionon the retina with the light rays emitted by the light source 100. Theilluminating optical system 200 comprises a first condenser lens 201, avariable diaphragm 202, a second condenser lens 203, a fixation pointfocusing lens 204, and a fixation point 205.

[0035] The variable diaphragm 202 is a light screening member. As shownin FIG. 1B, the variable diaphragm 202 is provided with a firstdiaphragm 202 a having an aperture in its peripheral portion, and asecond diaphragm 202 b having an aperture in its central portion. Thefirst diaphragm 202 a and the second diaphragm 202 b are arranged sideby side. The variable diaphragm 202 is moved in directions perpendicularto its optical axis by a signal provided by the controller 800 todispose either the first diaphragm 202 a or the second diaphragm 202 bon the optical path.

[0036] Accordingly, the variable diaphragm 202 of the illuminatingoptical system 200 is able to create a first illuminating state forillumination through a region around the center of the pupil of the eye1000 and a second illuminating state for illumination through theperiphery of the pupil of the eye 1000 at a point substantiallyconjugate with the pupil of the eye 1000.

[0037] The eye 1000 has the cornea 1100, the iris 1200 and the retina1300.

[0038] The variable diaphragm 202 reduces the influence of lightreflected by the cornea on measurement.

[0039] The reflected light guiding optical system 300 guides the lightrays reflected from the retina 1300 of the eye 1000 to the lightreceiving device 500. The reflected light guiding optical system 300comprises a first afocal lens 301, a second afocal lens 302, aconverting device 400 which converts the reflected light rays into atleast seventeen light beams, and a beam splitter 303.

[0040] The converting device 400 of the reflected light guiding opticalsystem 300 is conjugate with the variable diaphragm 202 of theilluminating optical system 200. The converting device 400 and thevariable diaphragm 202 are conjugate with the iris 1200.

[0041] The light reflected from the cornea can be prevented fromaffecting the measurement of refraction by using a screened portion ofthe illuminating optical system 200 for the measurement of refraction.

[0042] If the first diaphragm 202 a of the variable diaphragm 202 is onthe optical path, a region corresponding to the central screeningportion of the first diaphragm 202 a is measured. If the seconddiaphragm 202 b is disposed on the optical path, a region correspondingto a portion around the central aperture is measured.

[0043] The illuminating optical system 200 is constructed so that aminute region on the eyeground of the eye 1000 is illuminated by thelight emitted by the light source 100 according to the refracting powerof the eye 1000. The abnormal refraction of the eye 1000 can becorrected by moving a point light source illuminating system 200A forprojecting the light emitted by the light source 100, and anilluminating system including a fixation point projecting system 200 B.

[0044] The point light source illuminating system 200A comprises thefirst condenser lens 201, the variable diaphragm 202 and the secondcondenser lens 203. The fixation point projecting system 200B comprisesthe fixation point focusing lens 204 and the fixation point 205. Lightrays emitted by the point light source illuminating system 200A andlight rays emitted by the fixation point projecting system 2003 arecombined in coaxial light rays by a beam splitter 220.

[0045] The conjugate relationship between the light source 100 and thefixation point 205 is maintained. The illuminating optical system 200 ismoved to form images of the point light source and the fixation point205 on the retina 1300, and then the fixation point projecting system200B is moved slightly away from the beam splitter 220 by a signalprovided by the controller 800 to blur the image of the fixation point205.

[0046] A first diopter adjusting mechanism adjusts the diopters of thepoint light source illuminating system 200A and the fixation pointprojecting system 200B by moving the variable diaphragm 202 and thefixation point 205 respectively along their optical axes so that thelevel of light received by the light receiving device 500 is kept at amaximum.

[0047] One of the objects of the optical characteristic measuringapparatus 10000 in the first embodiment is the measurement of opticalcharacteristics in a state having. a specific refractive power at thefar point of accommodation, the near point of accommodation or a pointbetween the far point of accommodation and the near point ofaccommodation.

[0048] Accordingly, a mute region on the eyeground is illuminated withlight rays according to the variation of the refractive power of theeyes 1000 because, in measurement at the far point of accommodation, forinstance, the refractive powers of the eyes 1000 vary in the range of−25 D to 25 D (Diopter). Therefore, the light source 100, the pointlight source illuminating system 200A and the fixation point projectingsystem 200B are moved by signals provided by the controller 800.

[0049] The reflected light guiding optical system 300 is formed so thatthe light receiving surface of the light receiving device 500 and theiris 1200 of the eye 1000 are substantially in conjugate relationshipwith respect to the first afocal lens 301 and the second afocal lens302.

[0050] The converting device 400 will be described hereinafter. Theconverting device 400 included in the reflected light guiding opticalsystem 300 is a wavefront converting device which converts the reflectedlight rays into a plurality of light beams. The converting device 400has a plurality of micro Fresnel lenses arranged in a planeperpendicular to the optical axis.

[0051] The micro Fresnel lens will be described in detail.

[0052] A micro Fresnel lens is an optical element having annular bandsat height pitches for wavelengths and an optimized blaze at a focalpoint. A micro Fresnel lens which can be applied to the presentinvention has, for example, eight levels of optical path differencesproduced by semiconductor fine processing techniques, and is capable ofachieving focusing at a focusing efficiency of 98% when only primarylight is used.

[0053] The converting device 400 of the first embodiment is a wavefrontconverting device capable of converting the reflected light rays into atleast seventeen light beams.

[0054] The light receiving device 500 receives a plurality of lightbeams from the converting device 400. In the first embodiment, the lightreceiving device 500 is a CCD. The CCD may be a common CCD for TV use ora CCD having 2000×2000 elements for measurement use.

[0055] Although a CCD for TV use as the light receiving device 500 has alow resolution, the CCD for TV use is inexpensive and its output can beeasily given to a personal computer which is used generally for imageprocessing. NTSC image signals provided by a CCD and its driver can beeasily given to a personal computer through an NTSC image input port.

[0056] Although a CCD for measurement use having 2000×2000 elements isexpensive, analog signals representing measured values can be given to apersonal computer if a CCD for measurement use is employed.

[0057] Signals provided by a CCD can be converted into correspondingdigital signals, and the digital signals may be given to a personalcomputer.

[0058] The reflected light guiding optical system 300 establishessubstantially conjugate relationship between the iris 1200 of the eye1000 and the converting device 400.

[0059] The beam splitter 303 is inserted in the reflected light guidingoptical system 300 to direct the light transmitted by the illuminatingoptical system 200 toward the eye 1000, and to transmit the reflectedlight.

[0060] An image signal provided by the light receiving device 500 isgiven through a light receiving device driver 510 to the opticalcharacteristic calculating unit 600.

[0061] The principle of operation of the optical characteristiccalculating unit 600 which calculates the optical characteristics of theeye 1000 on the basis of the inclination of light rays determined by thelight receiving device 500 will be described hereinafter.

[0062] “No Relay Lens and Immovable: Optical Characteristics IncludingSpherical Component Are Measured”

[0063] Emmetropia: Parallel light rays are focused on the eyeground tomake a secondary light source on the eyeground emit parallel light rays.

[0064] Myopia: Convergent light rays are emitted.

[0065] Regular astigmatism: Astigmatism is measured.

[0066] Irregular astigmatism: High-order aberration is mixed.

[0067] A method of calculation will be described in detail.

[0068] As shown in FIG. 2, coordinate axes X and Y are set on theconverting device, and coordinate axes x and y are set on the lightreceiving device 500. Then, a wave surface is expressed by a polarcoordinate system or a rectangular coordinate system:

w(r, θ)=W(X, Y)  (1)

[0069] The (i, j)-th measured data is expressed by:

w(r _(i), θ_(j))=W(X _(i) , Y _(j))  (2)

The contents of the measured data will be explained later.

[0070] The wave surface is expressed by an approximate expression:

F(K, G, T, S, C, A, X, Y)=Constant (K)+Inclination (G, T, X,Y)+Spherical surface (S, X, Y)+Regular astigmatism (C, A, X, Y)  (3)

[0071] The components of this polynomial will be explained.

[0072] The constant term is K.

[0073] The inclination reflecting alignment error is:

Gr cos(θ−T)=G cos(T)X+G sin(T)Y  (4)

[0074] Spherical surface (Discussion concerning sign)

S±{square root}{square root over (S²r²)}= S±{square root}{square rootover (S²−(X²+Y²))}  (5)

[0075] Sign is when S “+” is negative and sign is “−” when S ispositive.

[0076] Regular Astigmatism (Discussion Concerning Sign) $\begin{matrix}{{{{Formula}\quad 2}\quad {{\left( {C^{2} \pm \sqrt{C^{2} - r^{2}}} \right){\cos^{2}\left( {\theta + A} \right)}} = {\left( {C \pm \sqrt{C^{2} - \left( {X^{2} + Y^{2}} \right)}} \right)\quad \left( \frac{{{\cos^{2}(A)}X^{2}} + {2\sin \quad (A)\cos \quad (A){XY}} + {{\sin^{2}(A)}Y^{2}}}{X^{2} + Y^{2}} \right)}}}\quad} & (6)\end{matrix}$

[0077] Sign is “+” when C is negative and sign is “−” when C ispositive.

[0078] The square sum of the residuals at each measurement point is:$\begin{matrix}{\sum\limits_{i,j}\quad \left\lbrack {{W\left( {X_{i},Y_{j}} \right)} - {F\left( {K,G,T,S,C,A,X_{i},Y_{j}} \right)}} \right\rbrack^{2}} & (7)\end{matrix}$

[0079] Values of K, G, T, S, C and A are determined so that a valuecalculated by Formula 3 is a minimum. The suffixes i and j denotes oneof the elements of the converting device 400. Practically, the datarepresents inclinations and hence the derivative of each wave surface isused for calculation because data measured by the optical characteristicmeasuring apparatus are the inclination of light rays.

[0080] The inclination of light rays can be directly determined by thedifferentiation of the wave surface by positional coordinates. Valuesmeasured by the wavefront sensor are transverse aberrations from areference.

[0081] It is generally known that the following relation holdsapproximately in FIG. 2. $\begin{matrix}{\frac{\partial{W\left( {X,Y} \right)}}{\partial X} = \frac{{dx}\left( {X,Y} \right)}{l}} & (8) \\{\frac{\partial{W\left( {X,Y} \right)}}{\partial Y} = \frac{{dy}\left( {X,Y} \right)}{l}} & (9)\end{matrix}$

[0082] where 1 is the distance between the converting device 400 and thelight receiving device 500.

[0083] “Wave Surface, and Transverse Aberration Measured by theWavefront Sensor”

[0084] Values dx(X, Y) and dy(X, Y) are calculated for each element ofthe converting device 400, having a center point at X, Y, in which dxand dy are distances along the x-axis and the y-axis between apredetermined origin on the light receiving device 500, and a point onthe light receiving device 500 where the light beam falls on the lightreceiving device 500. As shown in FIG. 2, an origin corresponding to oneelement of the converting device 400 is a point on the light receivingdevice 500 where the converted light rays can be measured when both thespherical component and the astigmatism component representing therefractive characteristic of the eye are diopter, and there is noresidual of irregular astigmatism, which will be described later.

[0085] Suppose that the position of each point is (X⁰, Y⁰) when S, C andA are zero and there is no residual aberration. Then,

dx(X _(i) , Y _(j))=x _(ij) x ⁰ _(ij)  (10)

dy(X _(i) , Y _(j))=y _(ij) −y ⁰ _(ij)  (11)

[0086] Therefore, at the time of using the differentiation, the squaresum of the residuals is: $\begin{matrix}{\sum\limits_{i,j}\left\lbrack {\left\{ {\frac{{dx}\left( {X_{i},Y_{j}} \right)}{l} - \left( \frac{\partial F}{\partial X} \right)_{({X_{i},Y_{j}})}} \right\}^{2} + \left\{ {\frac{{dy}\left( {X_{i},Y_{j}} \right)}{l} - \left( \frac{\partial F}{\partial Y} \right)_{({X_{i},Y_{j}})}} \right\}^{2}} \right\rbrack} & (12)\end{matrix}$

[0087] The parameters G, T, S and C of F which makes the residual aminimum may be determined by an appropriate nonlinear optimizing method,such as a method of attenuation least squares.

[0088] The values of K, G and T are considered to reflect measuringerrors. In an auto-refractometer, S, C and A are measured values.

[0089] Although signs of some terms in the expressions expressing aspherical surface and regular astigmatism are indefinite, combinationsmay be calculated individually and a case where the residual is thesmallest may be employed.

[0090] A Irregular Astigmatism Component

[0091] The differentiation residuals are irregular astigmatismcomponent.

[0092] The conventional auto-refractometer is unable to measure theresidual component, and a new piece of software is necessary.

[0093] When analyzing the residual, i.e., the irregular astigmatismcomponent,

[0094] (1) The residual is calculated and represented in the form of thesquare sum.

[0095] (2) The residual is divided into components by a method similarto a method known in the theory of aberration.

[0096] (3) All the deviations from the wave surface expressed by S, Cand A as a reference surface are provided.

[0097] In some cases, a reference wave surface expressed by S or areference wave surface represented by a plane is necessary to find outthe distortion of the wave surface if the irregular astigmatism islarge.

[0098] “Square Sum of Residuals”

[0099] The square sum of residuals is measured by using K, G, T, S, Cand A determined by the foregoing method. If the square sum of residualshas N rows and M columns, a measurement value of the square sum ofresiduals is obtained by dividing the square sum of residuals by a valueobtained by doubling the square of n=N×M. $\begin{matrix}\frac{\sum\limits_{i,j}\left\lbrack {\left\{ {\frac{{dx}\left( {X_{i},Y_{j}} \right)}{l} - \left( \frac{\partial F}{\partial X} \right)_{({X_{i},Y_{j}})}} \right\}^{2} + \left\{ {\frac{{dy}\left( {X_{i},Y_{j}} \right)}{l} - \left( \frac{\partial F}{\partial X} \right)_{({X_{i},Y_{j}})}} \right\}^{2}} \right\rbrack}{2n} & (16)\end{matrix}$

[0100] B Analysis of Components

[0101] Comatic aberration: r^((2n+1))cos(θ+T_(n)) (n=1, 2, . . . )

[0102] Spherical aberration: r^(2n) (n=2, 3, . . . )

[0103] High-order astigmatism: r^(2n)cos² (θ+A_(n)) (n=1, 2, . . . )

[0104] There is an important aberration of an order higher than that ofthe astigratism component in the dection of rotation

f(r)cos^(n)(θ+T_(n)) (n=3, . . . )

[0105] The parameters of these terms are determined by subtractingvalues contributed to the components of the inclination, the sphericalsurface and the regular astigmatism by G, T, S, C and A obtainedpreviously from the inclination of light rays The comatic aberration,the spherical aberration, the high-order astigmatism and othercontribution can be calculated.

[0106] C Output of Deviation from Reference Wave Surface

[0107] The distance dL between corresponding positions on the referencewave surface F′ and the actual wave surface F is indicated.

[0108] In the following description, Fb and Fr are obtained by removingterms of constants and inclination from F.

[0109] These are expressed by functions approximating wave surfaces.

(Reference wave surface)=W _(b)(X _(i) , Y _(j))=F _(b)(S, C, A, X _(i), Y _(j))

(Reconstructed wave surface)=W _(r)(X _(j) , Y _(j))=F _(r)(S, C, A,parameters of irregular astigmatism component, X _(i) , Y _(j))Δz_(ij)=W _(r)(X _(i) , Y _(j))−W _(b)(X _(i) , Y _(j))  (17)

[0110] All the indications can be expressed in a unit of wavelength or aunit of micrometer.

[0111] D Indication of Deviation of Power from Reference Wave Surface

[0112] (1) Power is calculated on the basis of the respective calculatedresiduals of the components.

[0113] (2) The inclination dependent only the residual component at thatpoint is determined on the basis of only the residual component.

[0114] (3) The inclination at that point calculated on the basis of thereference wave surface Wb is subtracted from the measured value, and thepower of a point is calculated on the basis of points, typically, eightor fifteen points, around the point.

[0115] As shown in FIG. 3, the power indicates directly a quantity andan orientation relating to the maximum and the minimum curvature at apoint on a geometrical curved surface. When light rays converge in aradius R of curvature, power is expressed by 1/R.

[0116] Meridional power is indicated by a method illustrated in FIGS. 4and 5.

[0117] Generally, regular astigmatism has a high power in the directionof the vertical meridian and a low power in the direction of thehorizontal meridian. Power is expressed in diopters.

[0118] The operation of the converting device 400 for converting thereflected light rays into at least seventeen light beams will bedescribed in detail.

[0119] When measuring the S, C and A component, the origin and one pointon a radius, the direction of rotation can be calculated on the basis ofdata on four points. Since at least information of an order higher thanthat by one order is necessary, seventeen measuring points, i.e., asummation of 2×8=16 points and the origin, are necessary.

[0120] Accordingly, the optical characteristic calculating unit 600determines the inclination of light rays from a position on rich theprimary light rays are converged by the plurality of micro Fresnellenses, and determines the optical characteristics of the eye 1000 onthe basis of the inclination of light rays.

[0121] A blurred image is formed at one point represented by data onreceived light rays if the converting device 400 does not use the microFresnel lenses, and hence the center of gravity of each point isdetermined.

[0122] Even if micro Fresnel lenses are used, the accuracy of positionmeasurement can be increased by observing an image intentionally blurredby the light receiving elements as shown in FIG. 6. The position of thecenter of gravity can be determined by making the projected light raysfall on a plurality of pixels on the light receiving surface and makingreference to the intensities of light rays fallen on the pixels.

[0123] The accuracy of position measurement not higher than {fraction(1/10)} of the element can be secured by thus calculating the positionof the center of gravity.

[0124] As shown in FIG. 7, since an image formed by light rays reflectedfrom the retina and an image formed by light rays reflected from thecornea are different in the degree of blur and hence those images can bediscriminated from each other.

[0125] In an arrangement shown in FIG. 7(a), FIG. 7(b) is a graphshowing the distribution of intensity of light rays reflected from theretina on the light receiving device 500, FIG. 7(c) is a graph showingthe distribution of intensity of light rays reflected from the cornea onthe light receiving device 500, and FIG. 7(d) is a graph produced bycombining distribution curves shown in FIGS. 7(b) and 7(c).

[0126] When discriminating the images from each other, a peak isdetected, a slice level slightly lower than that of the peak is set, andthe position of the light rays reflected from the retina is determinedwithout being affected by the light rays reflected from the cornea. Theposition of the light rays reflected from the retina can be determinedby using an appropriate filter.

[0127] The optical characteristic measuring apparatus may be providedwith a display unit 700 for displaying the results of arithmeticoperations carried out by the optical characteristic calculating unit600.

[0128] The display unit 700 are capable of displaying the opticalcharacteristics of the eye 1000 in the spherical component, the regularastigmatism component, the angle of the axis of the regular astigmatismcomponent, and the irregular astigmatism component, which are determinedby calculation by the optical characteristic calculating unit 600.

[0129] Examples will be given below.

[0130] (1) Display of irregular astigmatism component

[0131] The irregular astigmatism component indicates a comaticcomponent, a spherical aberration component and a high-order astigmatismcomponent.

[0132] (2) Display of irregular astigmatism component a deviation

[0133] The irregular astigmatism component indicates two-dimensionallydeviation from the wave surface consisting of only a spherical componentand a regular astigmatism component.

[0134] (3) Two-dimensional display of curvature of wave surface indiopters

[0135] Two-dimensional graphic display is possible. A point havingastigmatism has two curvatures. According to the teachings ofdifferential geometry, both are perpendicular to each other.

[0136] The display unit 700 is capable of graphically displaying theoptical characteristics of the eye 1000. The display unit 700 is capableof displaying a picture of the eye 1000 viewed from the front on an x-ycoordinate system and of mapping powers in, for example, diopters on anx-y coordinate system.

[0137] The display unit 700 is capable of displaying the deviations ofthe optical characteristics of the eye 1000 from those of the normaleye.

[0138] The display unit 700 is also capable of mapping the deviationsfrom a reference wave surface reproduced from the calculated values ofS, C and A on the order of wavelength on the x-y coordinate system.

[0139] The display unit 700 is capable of graphically displayingdeviations of the optical characteristics of the eye 1000 from those ofthe normal eye, and those data can be represented in contour.

[0140] The display represented in contour can be mapped by, for example,pseudocolors.

[0141] Although the converting device 400 employed in the firstembodiment is a Hartmann plate employing micro Fresnel lenses, theconverting device 400 may be a Hartmann plate employing honeycomb-shapedmicro Fresnel lenses as shown in FIGS. 19(a) and 19(b). Ahoneycomb-shaped converting device 400 a is constructed so that aportion on the optical axis of the reflected light guiding opticalsystem 300 is indicated by a signal provided by the light receivingdevice 500. A portion of the Hartmann plate on the optical axis of thereflected light guiding optical system 300 is chromium-plated to form ascreening portion.

[0142] The respective origins of the X-Y coordinate system on theconverting device 400 a and the x-y coordinate system on the lightreceiving device 500 can be easily determined on the basis of positionscorresponding to the screening portion of the converting device 400 inthe signal provided by the light receiving device 500.

[0143] Second Embodiment

[0144] The optical characteristic measuring apparatus 10000 in the firstembodiment includes the Hartmann plate provided with micro Fresnellenses as the converting device 400. An optical characteristic measuringapparatus 10000 in a second embodiment according to the presentinvention employs a liquid crystal device 410 as a converting device 400instead of the Hartmann plate provided with micro Fresnel lenses.

[0145] Apertures for passing light rays can be formed in an optionalportions of the liquid crystal device 410. For example, the resolutionof a liquid crystal device of the SVGA (super video graphics array)system is 800 dots by 600 dots.

[0146] As shown in FIG. 8, the liquid crystal device 410 is driven bythe following method.

[0147] The actions of the liquid crystal device 410 are similar to thoseof the converting device 410 employed in the first embodiment.

[0148] First, measurement 1 is carried out in this state.

[0149] Then, all apertures are shifted laterally by half the spatialperiod of the apertures and measurement 2 is carried out.

[0150] Subsequently, all the apertures are shifted longitudinally byhalf the spatial period. and measurement 3 is carried out.

[0151] All the apertures are shifted laterally by half the spatialperiod in a direction reverse to that in which the apertures wereshifted laterally in the first lateral shifting cycle and measurement 4is carried out.

[0152] Consequently, the number of measuring points is four times aslarge as the number of measuring points at the measurement 1.

[0153] Generally, the following is possible.

[0154] Suppose that the apertures are square apertures of a sizecorresponding to 10 dots by 10 dots for simplicity. Then, informationabout different positions on the iris can be obtained by shifting theapertures by a distance corresponding to one dot at a time.

[0155] Thus information about 791 dots by 691 dots can be obtained.

[0156] Third Embodiment

[0157] As shown in FIG. 9, an optical characteristic measuring apparatus30000 in a third embodiment according to the present invention uses R, Gand B light rays for the precision measurement of the optical system ofthe eye 1000. .Measurement using the center wavelengths of cones for thethree primaries.

[0158] (1) Two dichroic mirrors 900 are disposed between the last lensof a reflected light guiding optical system and a converting device 400,reflected light rays divided by wavelength into R, G and B light rays,and the R, G and B light rays are received by three light receivingdevices 500, respectively.

[0159] (2) A color CCD may be used as the light receiving device 500.

[0160] Light rays of the d line may be used for measurement when theoptical characteristic measuring apparatus is used in the USA.

[0161] Fourth Embodiment

[0162] Referring to FIGS. 10 and 11, an optical characteristic measuringapparatus 40000 in a fourth embodiment according to the presentinvention comprises a first light source 1110 which emits light rays ofa first wavelength, a first illuminating optical system 1100 forilluminating a minute region on the retina 1030 of the eye 1000 withlight rays emitted by the first light source 1110, a first reflectedlight guiding optical system 1200 for guiding light rays reflected bythe retina, a first converting device 1300 for converting the reflectedlight rays into at least seventeen light beams, a first light receivingdevice 1400 which receives a plurality of light beams from the firstconverting device 1300, a second light source 2110 which emits lightrays of a second wavelength different from the first wavelength, asecond illuminating -optical system 2100 which focuses light raysemitted by the second light source 2110 for illumination on a portion ofthe eye 1000 around the center of curvature of the cornea of the eye1000, a second reflected light guiding optical system 2200 for guidinglight rays reflected from the cornea of the eye 1000, a secondconverting device 2300 which converts the light rays reflected from thecornea into at least seventeen light beams, a second light receivingdevice 2400 which receives a plurality of light beams from the secondconverting device 2300, and an arithmetic unit 9100 which determines theoptical characteristics of the eye 1000 on the basis of the inclinationof light rays received by the first light receiving device 1400, anddetermines the shape of the cornea of the eye 1000 on the basis of theinclination of light rays received by the second light receiving device2400.

[0163] The first illuminating optical system 1100 illuminates a minuteregion on the retina of the eye 1000 with light rays emitted by thefirst light source 1110. The first illuminating optical system 1100comprises a first condenser lens 1120, a light screening member 1130 anda second condenser lens 1140.

[0164] The first illuminating optical system 1100 can be moved along itsoptical axis according to the refractive power of the eye 1000 to focuslight rays on the eyeground of the eye. The first illuminating opticalsystem 1100 of the optical characteristic measuring apparatus 40000 canbe moved along its optical axis in a distance range corresponding to arange of about −20 D to about +20 D.

[0165] It is desirable that the first light source 1110 is capable ofemitting light having a high spatial coherence and a low temporalcoherence. The first light source 1110 of the fourth embodiment is aSLD, which is a point light source having a high luminance.

[0166] The first light source 1110 need not be limited to the SLD; alaser which emits light having a high spatial coherence and a hightemporal coherence can be employed as the first light source 1110 if arotary diffuser or the like is inserted in an optical path to lower thespatial coherence and the temporal coherence properly.

[0167] Although both the spatial coherence and the temporal coherence ofthe light emitted by a light source such as LED are low, it can be us ifa pinhole or the like is disposed at a position corresponding to thelight source on the light path, provided that the SLD emits a largequantity of light.

[0168] The first wavelength of the light emitted by the first lightsource 1110 may be a wavelength in the infrared region, such as 840 nm.

[0169] The light screening member 1130 is used fir creating anilluminating state 1A in which the eye is illuminated through a portionthereof around the: pupil, and an illuminating state 1B in which the eyeis illuminated through a portion thereof around the center of the pupil.

[0170] The light screening member 1130 may be a variable diaphragmprovided with a first diaphragm having an aperture in its centralportion for creating the illuminating state 1B, and a second diaphragmhaving an aperture in its peripheral portion for creating theilluminating state LA.

[0171] A screened portion of the first illuminating optical system 1100is used for the measurement of refraction to achieve measurement withoutbeing affected by light rays reflected from the cornea.

[0172] When the first diaphragm of the variable diaphragm is disposed onthe optical path, a range corresponding to a central screened portion ismeasured. When the second diaphragm of the variable diaphragm isdisposed on the optical path, a range corresponding to a region aroundthe central aperture is measured.

[0173] The light screening member 1130 may be a liquid crystal devicecapable of forming an aperture in its central portion to set theilluminating state 1A and of forming an aperture in its peripheralportion to set the illuminating state 1B.

[0174] Accordingly, the light screening device 1130 of the firstilluminating optical system 1100 is at a point substantially conjugatewith the pupil of the eye 1000, and is capable of creating the firstilluminating state 1A for illumination through a region around thecenter of the pupil of the eye 1000 and the second illuminating state 1Bfor illumination through the periphery of the pupil of the eye 1000.

[0175] The eye 1000 has the cornea 1010, the iris 1020 and the retina1300.

[0176] The first reflected light guiding optical system 1200 guideslight rays reflected from the retina 1030 of the eye 1000 to the lightreceiving device. The first reflected light guiding optical system 1200comprises a first afocal lens 1210, a second afocal lens 1220, and afirst converting device 1300 for converting the reflected light raysinto at least seventeen light beams.

[0177] Movement of the first illuminating optical system 1100 and thefirst reflected light guiding optical system 1200 is coordinated so thatthe positional relation between the first illuminating optical system1100 and the first reflected light guiding optical system 1200 whichmakes a signal provided by the first light receiving device 1400 whenthe reflected light rays reflected from a point on which the light raysemitted by the first light source 1110 are focused fall thereon reach apeak is maintained. The first illuminating optical system 1100 and thefirst reflected light guiding optical system 1200 are moved indirections to increase the peak of the output signal of the first lightreceiving device 1400 and are stopped at positions where the intensityof the light rays falling on the first light receiving device 1400 is amaximum. Consequently, light rays emitted by the first light source 1110are focused on the retina 1030.

[0178] The first converting device 1300 of the first reflected lightguiding optical system 1200 is conjugate with the light screening member1130 of the first illuminating optical system 1100. The first convertingdevice 1300 and the light screening member 1130 are conjugate with theiris 1200.

[0179] The first reflected light guiding optical system 1200 is movedalong the optical axis according to the refractive power of the eye1000. The first light receiving device 1400 or the first convertingdevice 1300 is substantially conjugate with the cornea 1010.

[0180] As shown in FIG. 11, the arithmetic unit 9100 is connected to acontrol unit 9200 and carries out operations for calculating opticalcharacteristics according to instructions given thereto by the controlunit 9200.

[0181] The control unit 9200 controls the optical characteristicmeasuring apparatus including the arithmetic unit 9100. An alignmentprocessing unit 9300 controls an alignment process.

[0182] A display unit 9400 displays data provided by the arithmetic unit9100. The display unit 9400 is capable of displaying the calculatedoptical characteristics of the eye 1000 calculated by the arithmeticunit 9100 and the shape of the cornea 1010.

[0183] The arithmetic unit 9100 estimates the optical characteristics ofthe eye 100 from the shape of the cornea 1010, compares the estimatedoptical characteristics with measured optical characteristics determinedon the basis of the output of the first light receiving device 1400 tofind abnormal optical characteristics attributable to the shape of thecornea 1010. The optical characteristics can be calculated by a raytracing method or a simpler approximation method. The position of asecondary point source on the retina 1030 may use a model value from theS value of refraction measurement at that time.

[0184]FIG. 12 illustrates the connection of the components of theoptical characteristic measuring apparatus with electrical components.

[0185] The second illuminating optical system 2100 focuses light emittedby the second light source 2110 for illumination on a portion of the eye1000 around the center of curvature of the cornea 1010 of the eye 1000.

[0186] The second illuminating optical system 2100 is used forilluminating the cornea 1010 entirely and hence does not need anydiaphragm.

[0187] The second light source 2110 emits light of a second wavelengthof 780 nm different from the first wavelength 840 nm of the lightemitted by the first light source 1110.

[0188] The second wavelength of 780 nm is smaller than the firstwavelength of 840 nm. Light of a wavelength outside the wavelengthregion of visible light is less offensive to the eye.

[0189] After completing alignment, which will be described later, thesecond illuminating optical system 2100 focuses light emitted by thesecond light source 2110 through a beam splitter 2120 on the center ofcurvature of the cornea 1010.

[0190] The second reflected light guiding optical system 2200 comprisesan afocal lens 2210, and a second converting device 2300 which convertsthe reflected light rays into at least seventeen light beams.

[0191] The second reflected light guiding optical system 2200 guides thereflected light rays reflected from the cornea 1010 of the eye 1000 tothe light receiving device. In a state where alignment is completed, thesecond light receiving device 2400 or the second converting device 2300is substantially conjugate with the cornea 1010.

[0192] A fixation point optical system 3100 comprises a fixation pointimage forming lens 3110 and a fixation point 3120.

[0193] Light rays transmitted by the first illuminating optical system1100 and light rays transmitted by the fixation point optical system3100 are combined coaxially.

[0194] The fixation point optical system 3100 can be adjusted to show apattern to the eye 1000, to blur an image or to fix the line of sight ofthe eye 1000. The fixation point optical system 3100 can be moved alongits optical axis according to the refractive power of the eye 1000.

[0195] An XY alignment optical system 4100 comprises a third lightsource 4110, a lens 4120 and a two-dimensional imaging device 4130.

[0196] The XY alignment optical system 4100 makes a point sourcecoincide with a point near the vertex of the cornea 1010.

[0197] The third light source 4110 emits light of 940 nm in wavelength.

[0198] The two-dimensional imaging device 4130 may be either atwo-dimensional PSD (Position Sensing Detector) or a two-dimensionalCCD. An image of a point source is formed at the center of thetwo-dimensional aging device 4130.

[0199] A Z alignment optical system 5100 comprises a fourth light source5110, a collimator lens 5120, a condenser lens 5130 and a linear imagingdevice 5140.

[0200] The Z alignment optical system 5100 makes a point source coincidewith a point near the vertex of the cornea 1010.

[0201] The linear imaging device 5140 is a linear PSD, but may be animaging device of any suitable type.

[0202] The Z alignment optical system 5100 collimates light rays emittedby the fourth light source 5110 and illuminates the cornea 1010 withparallel light rays. The linear imaging device 5140 is disposed at apoint to receive light rays reflected by regular reflection on a planeincluding an illumination optical axis and a reflection optical axis.

[0203] The z alignment optical system 5100 is disposed so that theparallel light rays intersects the optical axis of the collimator lens5120 when positioned at a predetermined distance.

[0204] A first beam splitter 6100 is a semitransparent mirror, A secondbeam splitter 6200 is an optical element which reflects light of awavelength around 780 nm entirely, and transmits light of a wavelengthof a wavelength on the infrared side of 780 nm. A third beam splitter6300 is a low-pass filter which transmits light of a wavelength around840 nm and reflects light of a wavelength around 940 nm entirely.

[0205] The operation of the XY alignment optical system 4100 will bedescribed with reference to FIG. 13.

[0206] The third light source 4110 is turned on instep S1, The lens 4120focuses light rays on the cornea 1010 in step S2. The position of abright point is observed by the two-dimensional imaging device 4130 instep S3. Data is displayed on a monitor in step S4 if manual alignmentis selected. Data is sent to the control unit in step SS if automaticalignment is selected.

[0207] The operation of the Z alignment optical system 5100 will bedescribed with reference to Pig. 14. The fourth light source 5110 isturned on in step S1. Light rays are collimated by the collimator lens5120 and a portion of the eye 1000 around the vertex of the cornea 1010is illuminated with parallel light rays in step S2. A virtual image isformed in step S3, and the virtual image is projected on the linearimaging device 5140 by the condenser lens 5130 in step S4. The linearimaging device 5140 provides measured data on the position of thevirtual image in step S5 and sends the measured data on the position ofthe virtual image to the control unit in step S6.

[0208] Alignment will be described in detail with reference to FIG. 15.

[0209] Suppose that the lenses on the eye side of the movable lens ofthe reflected light guiding system form a objective lens group.Alignment can be achieved by disposing the objective lens group so thatthe front focal point of the objective lens group coincide with areference measuring plane of a front portion of the eye 1000 (exitpupil, the surface of the cornea).

[0210] The movable lens moves so that the front focal point of themovable lens coincides with a point where the measuring light raystraveled through the objective lens group intersect the optical axis.(The point is substantially conjugate with the center of curvature ofthe cornea 1010 when the shape of the cornea 1010 is measured, and issubstantially conjugate with the eyeground when the opticalcharacteristics are measured.) Consequently, substantially parallellight rays fall always on the light receiving device and a measuringregion on the reference measuring plane can be substantially fixed.

[0211] The accurate position of the light rays on the referencemeasuring plane of the front portion of the eye 1000 can be determinedby measuring the coordinates of the light rays at a point conjugate withthe reference measuring plane of the front portion of the eye 1000 afterthe movable lens on the basis of data on the position at which lightrays fall on the light receiving device by interpolation orextrapolation, and dividing the coordinates of the light rays by thelateral magnification of the optical system.

[0212] FIGS. 15(a), 15(b), 15(c) and 15(d) illustrates a state formeasuring the shape of the cornea 1010, a state for measuring theoptical characteristics, a state for measuring emmetropia and a statefor measuring myopia, respectively, in which the measuring region on thereference measuring plane is substantially fixed.

[0213] The first converting device 1300 will be described.

[0214] The first converting device 1300 included in the first reflectedlight guiding optical system 1200 is a wavefront converting member whichconverts the reflected light rays into a plurality of light beams. Thefirst converting device 1300 has a plurality of micro Fresnel lensesarranged in a plane perpendicular to the optical axis thereof.

[0215] Micro Fresnel lenses will be described in detail.

[0216] A micro Fresnel lens is an optical element having annular bandsat height pitches for wavelengths and an optimized blaze at a focalpoint. A micro Fresnel lens which can be applied to the presentinvention has, for example, eight levels of optical path differencesproduced by semiconductor fine processing techniques, and is capable ofachieving focusing at a focusing efficiency of 98% when only primarylight is used.

[0217] In the fourth embodiment, the first converting member 1300 is awavefront converting device capable of converting the reflected lightrays into at least seventeen light beams.

[0218] The second converting device 2300 is similar to the firstconverting device 1300 and hence the description thereof will beomitted.

[0219] The first light receiving device 1400 receives a plurality oflight beams from the first converting device 1300. In the fourthembodiment, the light receiving device 1400 is a CCD. The CCD may be acommon CCD for TV use or a CCD having 2000×2000 elements for measurementuse.

[0220] Although a CCD for TV use as the first light receiving device1400 has a low resolution, the CCD for TV use is inexpensive and itsoutput can be easily given to a personal computer which is usedgenerally for image processing. NTSC image signals provided by a CCD andits driver can be easily given to a personal computer through an NTSCimage input port.

[0221] Although a CCD for measurement use having 2000(2000 elements isexpensive, analog signals representing measured values can be given to apersonal computer if a CCD for measurement use is employed.

[0222] Signals provided by a CCD can be converted into correspondingdigital signals, and the digital signals may be given to a personalcomputer.

[0223] The first light receiving device 1400 is substantially conjugatewith the first converting device 1300 and the iris 1020 of the eye 1000.

[0224] The first reflected light guiding optical system 1200 maintainsthe substantially conjugate relation between the first converting device1300 and the iris 1020 and may be provided with an adjusting system forcarrying out adjustment so that the reflected light rays from theeyeground fall in substantially parallel light rays on the lightreceiving device in a first light receiving state, and the reflectedlight rays from the cornea 1010 fall in substantially parallel lightrays on the light receiving device in a second light receiving state.

[0225] The first beam splitter 6100 is inserted in the first reflectedlight guiding optical system 1200 to direct the light transmitted by theilluminating optical system 1100 toward the eye 1000, and to transmitthe reflected light.

[0226] The second light receiving device 2400 is the same inconfiguration and actions as the first light receiving device 1400 andhence the description thereof will be omitted.

[0227] The principle of operations of the arithmetic unit 9100 fordetermining the optical characteristics of the eye 1000 on the basis ofthe inclination of light rays provided by the first light receivingdevice 1400 will be described in detail.

[0228] An algorithm will be described in detail.

[0229] As shown in FIG. 2, coordinate axes X and Y are set on the firstconverting device 1300, and coordinate axes x and y are set on the firstlight receiving device 1400. Then, a wave surface is expressed by apolar coordinate system or a rectangular coordinate system.

X=(X′/β)  (1)

Y=(Y′/β)  (2)

[0230] where β is the lateral magnification of the optical system.

[0231] If the optical system does not cause aberration, the relationbetween wavefront aberrations W(X, Y) and W′(X′, Y′) is expressed by:

W{(X′/β), (Y′/β)}=W′(X′, Y′)  (3)

[0232] The following appropriate polynomial is given.

[0233] f(X, Y, Z . . . ; A, B, C . . . ) where X, Y, Z, . . . arequantities determined by coordinates, and A, B, C . . . are parameters.

[0234] Expression of a wave surface by the polynomial f will beexamined; that is, optimum parameters (A, B, C, . . . ) are calculated.

[0235] From the Hartmann's measuring principle, $\begin{matrix}{{\frac{\partial{W\left( {X^{\prime},Y^{\prime}} \right)}}{\partial X^{\prime}} = \frac{{dx}\left( {X^{\prime},Y^{\prime}} \right)}{l}}{\frac{\partial{W\left( {X^{\prime},Y^{\prime}} \right)}}{\partial Y^{\prime}} = \frac{{dy}\left( {X^{\prime},Y^{\prime}} \right)}{l}}} & (4)\end{matrix}$

[0236] Practically, data represents an inclinations and hence thederivative of each wave surface is used for calculation. In the presentinvention, measured data represents the inclination of light rays. Theinclination can be determined by directly differentiating the wavesurface at the coordinates of a position.

[0237] The wavefront sensor measures a lateral residual from areference.

[0238] It is known that the following relation holds good in FIG. 2, inwhich 1 is the distance between the first converting device 1300 and thefirst light receiving device 1400. Values dx(X, Y) and dy(X, Y) arecalculated for each element of the first converting device 1300, havinga center point at X, Y, in which dx and dy are distances along thex-axis and the y-axis between a predetermined origin on the first lightreceiving device 1400, and a point on the first light receiving device1400 where the light beam falls on the first light receiving device1400.

[0239] An origin corresponding to one element of the first convertingdevice 1300 is a point on the first light receiving device 1400 wherethe converted light rays can be measured when the wave surface isuniformly flat, i.e., both the spherical component and the astigmatismcomponent representing the refractive characteristic of the eye are 0diopter, and there is no residual of irregular astigmatism.

[0240] Suppose that dx and dy are deviations of the light beam from thereference point. Then,

dx(X _(i) , Y _(j))=x _(ij) −x ⁰ _(ij)  (5)

dy(X _(i) , Y _(j))=y_(ij) −y ⁰ _(ij)  (6)

[0241] An expression, (number of measured data)×2, can be obtained bysubstituting f into the expressions (5), (6), and necessary parameterscan be obtained by method of least squares.

[0242] Although the constant term of f cannot be determined because anexpression obtained by differentiating f is used, the determination ofnecessary parameters is sufficient for the present invention.

[0243] Concretely, the Zernike's polynomial, i.e., an orthogonalfunction properly representing aberration in terms of geometricaloptics, may be used.

[0244] The general term of the Zernike's polynomial is expressed by:$\begin{matrix}{{{Z_{nm}^{*}\left( {r,\theta} \right)} = {{R^{m,{lm}}(r)}\left\{ \frac{\sin}{\cos} \right\} \left( {n - {2m}} \right)\theta}}{{{{SIN}\quad {FOR}\quad n} - {2m}} > 0}{{{{{{COS}\quad {FOR}\quad n} - {2m}} \leqq 0}\because{R^{m,{2m}}(r)}} = {\sum\limits_{m = 1}^{m}{\left( {- 1} \right)^{2}\frac{\left( {n - s} \right)!}{{s!}{\left( {m - s} \right)!}{\left( {n - m - s} \right)!}}r^{n - {2s}}}}}} & (7)\end{matrix}$

[0245] More specifically, the Zernike's polynomial is expressed by thefollowing expressions.

Z ₀₀=1

Z ₁₀ =x

Z ₁₁ =y

Z ₂₀=2xy

Z ₂₁=−1+2y ²+2x ²

Z ₂₂ =y ² −x ²

Z ₃₀=3xy ² −x ³

Z ₃₁=−2x+3xy ²+3x ³

Z ₃₂=−2y+3y ³+3x ² y

Z ₃₃ =y ³−3x ² y

Z ₄₀=4y ³ x+4x ³ y

Z ₄₁=−6xy+8y ³ x+8x ³ y

Z ₄₂=1−6y ²−6x ²+6y ⁴+12x ² y ²+6x ⁴

Z ₄₃=−3y ²+3x ²+4y ⁴−4x ⁴

Z ₄₄ =y ⁴−6x ² y ² +x ⁴

[0246] Seventeen sample points (at least sixteen sample points on fourrows along the X-is and four columns along the Y-axis, and one samplepoint) or above are necessary when those expressions are combined byfourth degree.

[0247] Algorithm will be concretely described with reference to FIG. 16.

[0248] In step S1, sample data is produced on the basis of he dataprovided by the first light receiving device 1400. A defocus componentand an inclination component are determined by method of least squaresin step S2. The defocus component and the inclination component aresubtracted from the sample data in step S3. In step S4, a referencecurvature is determined on the basis of D and the position of themovable lens. In step S5, A is determined by method of least squares. Instep S6, a query is made to see if the shape of the cornea is beingmeasured. If the response in step S6 is affirmative, the value of f ismultiplied by ½ in step S7 because the light rays are reflected twice,and mapping is executed in step so.

[0249] If the response in step S6 is negative, step S7 is skipped andstep $8 is executed

[0250] Fifth Embodiment

[0251] An optical characteristic measuring apparatus 50000 in a fifthembodiment according to the present invention for measuring the opticalcharacteristics of the eye can be set for a first state for measuringthe optical characteristics of the eye as shown in FIG. 17 or a secondstate for measuring the shape of the cornea as shown in FIG. 18, and iscapable of carrying out measurement for both determining the opticalcharacteristics of the eye and determining the shape of the cornea ofthe eye with common devices.

[0252] The optical characteristic measuring apparatus 50000 comprises alight source 1110, an illuminating optical system 1100 for illuminatinga minute region In the eye with light rays emitted by the light source1110, a reflected light guiding optical system 1200 for guiding lightrays reflected from the eye to a light receiving device 1400, aconverting device 1300 converting the reflected light rays into at leastseventeen light beams and gives the light beams to the light receivingdevice 1400, and an arithmetic unit which determines the opticalcharacteristics of the eye and the shape of the cornea of the eye on thebasis of the inclination of light rays provided by the light receivingdevice 1400.

[0253] The illuminating optical system 1100 comprises a first condenserlens 1120, a light screening member 1130 and: a second condenser lens1140.

[0254] The illuminating optical system 1100 can, be moved along itsoptical axis according to the refractive power of the eye in a distancerange corresponding to a range of about −20 D to about +50 D so thatlight rays are focused on the eyeground of the eye. The illuminatingoptical system 1100 is moved to a position corresponding to +50 D forthe measurement of the shape of the cornea.

[0255] The wavelength of light emitted by the light source 1110 may bethat in the infrared region, such as 840 nm.

[0256] The light screening member 1130 sets different illuminatingstates respectively for the measurement or the eyeground the opticalcharacteristics of the eyes and a the measurement of the shape of thecornea.

[0257] The illuminating optical system 1100 can be moved according tothe refractive power of the eye so that a first illuminating state isset to illuminate a minute region on the eyeground of the eye with lightemitted by the light source 1110 to measure the eyeground the opticalcharacteristics of the eyes or so that a second illuminating state isset to focus light emitted by the light source 1110 on a portion of theeye around the center of curvature of the cornea to measure the shape ofthe cornea.

[0258] When measuring the eyeground, an illuminating state. 1A, in whichthe eye is illuminated through a portion thereof around the pupil, or anilluminating state 1B, in which the eye is illuminated through a portionthereof around the center of the pupil, is created.

[0259] When measuring the shape of the cornea, an ND filter is insertedin the optical path to create a second illuminating state to make thequantity of received light uniform because the reflectivity of thecornea is higher than that of the retina.

[0260] The light screening member 1130 may be a variable diaphragmprovided with a first diaphragm having an aperture in its centralportion, and a second diaphragm having an aperture in its peripheralportion.

[0261] When the first diaphragm of the variable diaphragm is inserted inthe optical path, a region screened by the central screening portion ismeasured. When the second diaphragm of the variable diaphragm isinserted in the optical path, a region corresponding to a portion aroundthe central aperture is measured.

[0262] The light screening member 1130 may be a liquid crystal devicecapable of forming an aperture in its central portion to set theilluminating state 1A and of forming an aperture in its peripheralportion to set the illuminating state 1B.

[0263] Accordingly, the light screening device 1130 is at a pointsubstantially conjugate with the pupil of the eye, and is capable ofcreating the first illuminating state 1A for illumination through aregion around the center of the pupil of the eye and the secondilluminating state 1B for illumination through the periphery of thepupil of the eye.

[0264] The reflected light guiding optical system 1200 guides light raysreflected from the eye to the light receiving device. The reflectedlight guiding optical system 1200 comprises a first afocal lens 1210, asecond afocal lens 1220, and a converting device 1300 for converting thereflected light rays into at least seventeen light beams.

[0265] The illuminating optical system 1100 guides the light rays to thelight receiving device 1400 at a position substantially conjugate withthe retina of the eye in a first light receiving state, and to guide thelight rays to the light receiving device 1400 at a positionsubstantially conjugate with the cornea of the eye in a second lightreceiving state.

[0266] Movement of the illuminating optical system 1100 and thereflected light guiding optical system 1200 is coordinated so that thepositional relation between the illuminating optical system 1100 and thereflected light guiding optical system 1200 which makes a signalprovided by the light receiving device 1400 when the reflected lightrays reflected from a point on which the light rays emitted by the lightsource 1110 are focused fall thereon reach a peak is maintained. In thefifth embodiment, the illuminating optical system 1100 and the reflectedlight guiding optical system 1200 are moved in a distance rangecorresponding to a diopter range of −20 D to +50 D. Positionscorresponding to about +50 D is used for the measurement of the shape ofthe cornea. Thus, the light rays emitted by the first light source 1110is focused on the retina. The illuminating optical system 1100 and thereflected light guiding optical system 1200 are moved in directions toincrease the peak of the output signal of the first light receivingdevice 1400 and are stopped at positions where the intensity of thelight rays falling on the light receiving device 1400 is a maximum.

[0267] The reflected light guiding optical system 1200 can be movedalong its optical axis according to the refractive power of the eye sothat substantially parallel light rays fall on the converting device1300.

[0268] Thus, in the fifth embodiment, the light receiving device 14 isused for both the measurement of the optical characteristics of the eyeand the measurement of the shape of the cornea, so that the cost of theoptical characteristic measuring apparatus is reduced.

[0269] The fifth embodiments are the same in other respects inconstitution functions and operations as the first embodiment and hencethe further description thereof will be omitted.

[0270] As is apparent from the foregoing description, the opticalcharacteristic measuring apparatus of the present invention is capableof measuring the optical characteristics of the eye including irregularastigmatism and of measuring the shape of the cornea of the eye.

What is claimed is:
 1. An optical characteristic measuring apparatuscomprising: a light source: an illuminating optical system forilluminating a minute region on the retina of the eye with light raysemitted by the light source; a light receiving device; a reflected lightguiding optical system for guiding reflected light rays reflected fromthe retina of the eye to the light receiving device; a converting devicecapable of converting the reflected light rays into at least seventeenlight beams and giving the light beams to the light receiving device;and an optical characteristic calculating unit for determining theoptical characteristics of the eye on the basis of data provided by thelight receiving device and representing an inclination of light rays. 2.An optical characteristic measuring apparatus comprising: a lightsource: an illuminating optical system for illuminating a minute regionon the retina of the eye with light rays emitted by the light source; alight receiving device; a reflected light guiding optical system forguiding reflected light rays reflected from the retina of the eye to thelight receiving device; a converting device capable of converting thereflected light rays into at least seventeen light beams and giving thelight beams to the light receiving device; an optical characteristiccalculating unit for determining the optical characteristics of the eyeincluding a spherical component, a regular astigmatism component, theangle of the axis of the regular astigmatism component, and an irregularastigmatism component on the basis of data provided by the lightreceiving device and representing an inclination of light rays; and adisplay unit for displaying the optical characteristics of the eyeincluding the spherical component, the regular astigmatism component,the angle of the axis of the regular astigmatism component, and theirregular astigmatism component.
 3. The optical characteristic measuringapparatus according to claim 2 , wherein the display unit is capable ofgraphically displaying the deviations of the optical characteristics ofthe eye from those of the normal eye or the optical characteristicsincluding refractive power of the eye.
 4. The optical characteristicmeasuring apparatus according to claim 1 or 2 , wherein the convertingdevice comprises a plurality of micro Fresnel lenses arranged in a planeperpendicular to its optical axis, and the optical characteristiccalculating unit determines an inclination of reflected light rays froma position on the light receiving surface of the light receiving deviceon which the reflected light rays are converged, and determines theoptical characteristics of the eye on the basis of the inclination. 5.The optical characteristic measuring apparatus according to claim 1 ,wherein the optical characteristic calculating unit discriminatesbetween reflected light rays reflected from the retina and thosereflected from the cornea on the basis of a mode of distribution of thereflected light rays on the light receiving device, and determines theoptical characteristics of the eye on the basis of the inclination ofthe reflected light rays reflected from the retina.
 6. The opticalcharacteristic measuring apparatus according to claim 3 , wherein thereflected light guiding optical system is constructed so that the lightreceiving device is dislocated slightly from a position conjugate withthe eyeground of the eye or so that the converting device and the irisof the eye are in conjugate relationship.
 7. The optical characteristicmeasuring apparatus according to claim 1 or 2 , wherein the reflectedlight guiding optical system has an adjusting function to maintain theconjugate relationship between the converting device and the iris of theeye and to make the reflected light rays reflected from the eyegroundsubstantially parallel light rays.
 8. The optical characteristicmeasuring apparatus according to claim 1 or 2 , wherein the illuminatingoptical system is adjusted according to the refractive power of the eyeso as to illuminate a minute region on the eyeground of the eye with thelight rays emitted by the light source.
 9. The optical characteristicmeasuring apparatus according to claim 1 or 2 , wherein the illuminatingoptical system is provided with a light screening member capable ofcreating a first illuminating state in which the eye is illuminatedthrough a portion thereof around the center of the pupil, and a secondilluminating state in which the eye is illuminated through a portionthereof around the pupil.
 10. optical characteristic measuring apparatusaccording to claim 1 or 2 , wherein the converting device is a liquidcrystal device capable of forming a plurality of apertures.
 11. Theoptical characteristic measuring apparatus according to claim 10 ,wherein the converting device is a liquid crystal device capable offorming a plurality of apertures at desired positions, and the opticalcharacteristic calculating unit determines the optical characteristicsof the eye accurately on the basis of inclinations of light raystraveled through the apertures formed respectively at differentpositions.
 12. An optical characteristic measuring apparatus comprising:a first light source which emits light rays of a first wavelength: afirst illuminating optical system for illuminating a minute region onthe retina of the eye with light rays emitted by the first light source;a first light receiving device; a first reflected light guiding opticalsystem for guiding reflected light rays reflected from the retina of theeye to the first light receiving device; a first converting devicecapable of converting the reflected light rays reflected from the retinainto at least seventeen light beams and giving the light beams to thefirst light receiving device; a second light source which emits lightrays of a second wavelength different from the first wavelength; asecond illuminating optical system for illuminating a portion of the eyearound the center of curvature of the cornea of the eye with light raysemitted by the second light source; a second light receiving device; asecond reflected light guiding optical system for guiding reflectedlight rays reflected from the cornea of the eye to the second lightreceiving device; a second converting device capable of converting thereflected light rays reflected from the cornea into at least seventeenlight beams and giving the light beams to the second light receivingdevice; and an arithmetic unit for determining the opticalcharacteristics of the eye on the basis of data provided by the firstlight receiving device and representing an inclination of light rays,and determining the shape of the cornea of the eye on the basis of dataprovided by the second light receiving device and representing aninclination of light rays.
 13. The optical characteristic measuringapparatus according to claim 12 further comprising a display unit fordisplaying data provided by the arithmetic unit including the opticalcharacteristics of the eye and the shape of the cornea.
 14. The opticalcharacteristic measuring apparatus according to claim 12 wherein thearithmetic unit estimates the optical characteristics of the eye fromthe shape of the cornea by calculation, compares the estimated opticalcharacteristics with the optical characteristics determined on the basisof the output of the first light receiving device to decide abnormaloptical characteristics due to factors other than the shape of thecornea.
 15. The optical characteristic measuring apparatus according toclaim 12 , wherein the converting device comprises a plurality of microFresnel lenses arranged in a plane perpendicular to its optical axis,and the arithmetic unit determines the inclination of the reflectedlight rays from a position on the light receiving surface of the firstlight receiving device on which the reflected light rays are converted,and determines the optical characteristics of the eye on the basis ofthe inclination.
 16. An optical characteristic measuring apparatuscomprising: a light source which emits illuminating light rays: anilluminating optical system capable of illuminating the eye selectivelyin a first illuminating state in which a minute region on the retina ofthe eye is illuminated with light rays emitted by the light source or ina second illuminating state in which a portion of the eye around thecenter of curvature of the cornea of the eye is illuminated with lightrays emitted by the light source; a light receiving device; a reflectedlight guiding optical system for guiding reflected light rays reflectedfrom the eye to the light receiving device in a first guiding state inwhich the reflected light rays are received at a position substantiallyconjugate with the retina of the eye or in a second guiding state inwhich the reflected light rays are received at a position substantiallyconjugate with the cornea of the eye; a converting device capable ofconverting the reflected light rays into at least seventeen light beamsand giving the light beams to the light receiving device; and anarithmetic unit which determines the optical characteristics of the eyeon the basis of an inclination of the light rays received by the lightreceiving device in the first illuminating state and the first guidingstate, and determines the shape of the cornea on the basis of aninclination of the reflected light rays received by the light receivingdevice in the second illuminating state and the second guiding state.17. The optical characteristic measuring apparatus according to claim 16, wherein the reflected light guiding optical system is provided with anadjusting means capable of adjusting the reflected light guiding opticalsystem so that the reflected light rays reflected from the eyeground ofthe eye fall on the light receiving device in substantially parallellight rays in the first guiding state and so that the reflected lightreflected from the cornea of the eye fall on the light receiving devicein substantially parallel light rays.
 18. The optical characteristicmeasuring apparatus according to claim 16 , wherein the illuminatingoptical system is adjusted according to the refractive power of the eyeso as to illuminate a minute region on the eyeground of the eye with thelight rays emitted by the light source in the first illuminating sate,and to focus the light rays emitted by the light source on a portion ofthe eye around the center of curvature of the cornea of the eye in thesecond illuminating state.
 19. The optical characteristic measuringapparatus according to claim 16 , wherein the illuminating opticalsystem is provided with a light screening member which creates either anilluminating state 1A in which the eye is illuminated through a portionthereof around the pupil or an illuminating state 1B in which the eye isilluminated through a portion thereof around the center of the pupil inthe first illuminating state.
 20. The optical characteristic measuringapparatus according to any one of claims 1 to 19 , wherein theconverting device is formed in a shape such that a portion coincidingwith the optical axis of the reflected light guiding optical system canbe found from a signal provided by the light receiving device.